Trace Minerals for California Beef Cattle 

University of California, Cooperative Extension

Selenium

    Selenium (Se) was identified as an essential nutrient for beef cattle in the late 1950's. Prior interest in Se concerned cattle receiving too much Se. In the last thirty years more problems with Se deficiency, than excess, have been identified worldwide. Both problems tend to be regional or localized conditions. Deficiencies or excesses occur when cattle diets are composed only of Se deficient or excess feeds. This is common when cattle are on a single source of feed, such as hay from a deficient source or pasture irrigated with excess Se in the water and/or soil.

A sign of Se deficiency in beef cattle is nutritional myodegeneration particularly affecting the heart muscle and producing a disease commonly called white muscle disease. In this disease, white sections are observed in heart muscle. Lameness and/or death can also occur with Se deficiency. Other symptoms of inadequate Se may be reduced weight gain, poor feed conversion, diarrhea, reduced reproduction (particularly retained placenta) and lowered immune response. Rough hair coats and general "ill-thrift" may also be observed. Due to effective diagnostic and supplementation methods, Se deficiency can be identified and economically corrected.

Normal blood Se levels are 0.10 to 0.20 ppm.  Marginal levels are 0.05 to 0.08 ppm.  Symptoms of frank deficiency, such as white muscle disease, are to be expected when blood Se levels fall below 0.05 ppm.  Cattle should be supplemented when blood Se levels are below 0.08 ppm. Responses of deficient cattle to Se supplementation may include increased weight gain, reduced scours, improved feed efficiency, fewer retained placenta and improved immune response.

Long-term whole blood Se levels of 2.0 ppm have not been excessive but due to possible antagonisms with other trace minerals, whole blood Se levels are ideally not above 0.40 ppm.

Selenium does cross the placenta and newborn calves will have higher Se levels than their dams. Calves from Se deficient cows or Se marginal cows become deficient fairly soon (before 5 months of age).  This is because Se is not efficiently transferred through the milk. Cattle can become Se deficient in 30 to 45 days following Se supplementation by injection or changing to Se deficient feeds.

Selenium deficiency is freqeuntly observed on soils of volcanic origin. Selenium deficiency should always be suspected on volcanic soils.

Excess Se can be harmful. Cattle have a large tolerance for Se and under ranch conditions are generally not exposed to excess Se. In carefully controlled, planned experiments to investigate safety of rumen Se boluses, up to eight (8) boluses, four times the recommended amount, have been given at one time without harmful effects to cattle. Potential harm to wildlife and the environment will be avoided by using all Se products according to label directions. Extensive testing of the environment shows use of Se supplements for livestock does not pose problems.